<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <link href="https://unpkg.com/element-ui/lib/theme-chalk/index.css" rel="stylesheet">
  <style>
    *{
      margin: 0;
      padding: 0;
      border: 0;
      outline: none;
      font-family: Arial;
      list-style: none;
      -webkit-font-smoothing: antialiased;
    }
    html, body, #app{
      height: 100%;
    }
    #app{
      padding: 20px 0;
      box-sizing: border-box;
    }
    .wrapper{
      display: flex;
      height: 100%;
      overflow: hidden;
      max-width: 1200px;
      margin: 0 auto;
    }
    .menu{
      width: 100px;
      height: 100%;
      padding-right: 20px;
    }
    .content{
      flex: 1;
      height: 100%;
      overflow: hidden;
      position: relative;
    }
    .menu-item{
      margin-bottom: 10px;
    }
    .menu-item-content{
      width: 100%;
      padding: 7px 0;
      text-align: center;
      border: 1px solid #ddd;
      border-radius: 2px;
      color: #333;
      cursor: pointer;
    }
    .active{
      border-color: #409EFF;
      background: #409EFF;
      color: #fff;
    }
    .content-item{
      margin-bottom: 20px;
    }
    .content-item-text{
      border-radius: 2px;
      border: 1px solid #ddd;
    }
    .content-item-text>img{
      width: 100%;
      vertical-align: middle;
    }
  </style>
</head>
<body>
    <div id="app">
      <div class="wrapper">

        <div class="menu">
          <ul>
            <li class="menu-item" v-for="(item, index) in menu" :key="index" @click="handleClick(index)">
              <div class="menu-item-content" :class="{'active': getCurrentIndex() == index}" v-text="item.label"></div>
            </li>
          </ul>
        </div>

        <div class="content" ref="content">
          <ul>
            <li class="content-item" v-for="(item, index) in content" :key="index">
              <div class="content-item-text">
                <img :src="item" alt="">
              </div>
            </li>
          </ul>
        </div>
        
      </div>
    </div>
  <script src="https://cdn.jsdelivr.net/npm/better-scroll"></script>
  <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
  <script src="https://unpkg.com/element-ui/lib/index.js"></script>
  <script>
    new Vue({
      el: '#app',
      data: {
        contentScroll: null,
        listHeight: [], // 用来存储每一个子盒子的高度
        currentIndex: 0,
        scrollY: 0,
        menu: [
          {
            label: '图片一',
            id: 0,
          },
          {
            label: '图片二',
            id: 1,
          },
          {
            label: '图片三',
            id: 2,
          },
          {
            label: '图片四',
            id: 3,
          },
          {
            label: '图片五',
            id: 4,
          },
        ],
        content: [
          'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1575539093143&di=d3d787658bd0b0f21d2459d90b3bd19b&imgtype=jpg&src=http%3A%2F%2Fimg4.imgtn.bdimg.com%2Fit%2Fu%3D1735688044%2C4235283864%26fm%3D214%26gp%3D0.jpg',
          'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1575539192878&di=f46b69a4c2db2ba2f07f0fe1cc7af952&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201210%2F04%2F20121004231502_NrBQG.jpeg',
          'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1575539157019&di=122152eaee12d6ea019b2cec2b80e468&imgtype=0&src=http%3A%2F%2Fpic44.nipic.com%2F20140723%2F18505720_094503373000_2.jpg',
          'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1575539175569&di=d33d35a826cc700add7b7bd53f9282c0&imgtype=0&src=http%3A%2F%2Fpic37.nipic.com%2F20140103%2F10616010_215644481373_2.jpg',
          'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1575539212191&di=ec438ea6559d06cc1a49a27b122e8edf&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fblog%2F201312%2F09%2F20131209151602_evtcw.jpeg',
        ]
      },
      methods: {
        initScroll() {
          const content = this.$refs.content;
          this.contentScroll = new BScroll(content, {
            click: true, // 因为betterscroll默认会阻止点击事件。这里要设置一下
            mouseWheel: true, // 鼠标滚轮滚动
            probeType: 3,
            scrollY: true,
            scrollbar: {
              fade: true, // 是否显示滚动条
              interactive: false, // 1.8.0 新增
            },
            preventDefault: false, // 阻止了浏览器默认选中行为
          });
          // 获取滚动的值，赋值给scrollY
          this.contentScroll.on('scroll', pos => {
            this.scrollY = Math.abs(Math.round(pos.y));
          });
        },
        getCurrentIndex() {
          for (let i = 0; i < this.listHeight.length; i++) {
            const height = this.listHeight[i];
            const height1 = this.listHeight[i + 1];
            // 解决当滚动到最后时，内容不足盒子高度时，菜单显示问题。当滚动到最后，选中最后一个菜单
            // maxScrollY：最大纵向滚动位置
            if (Math.abs(this.contentScroll.maxScrollY) === Math.abs(this.scrollY)) {
              return this.content.length - 1;
            }
            if (!height1 || (this.scrollY < height1 && this.scrollY >= height)) {
              return i;
            }
          }
        },
        handleClick(index) {
          const content = this.$refs.content;
          const contentList = content.getElementsByClassName('content-item');
          const el = contentList[index];
          // scrollToElement：滚动到目标元素
          this.contentScroll.scrollToElement(el, 300);
        },
        getHeightList() {
          this.listHeight = [];
          let height = 0;
          this.listHeight.push(height);
          const content = this.$refs.content;
          const contentList = content.getElementsByClassName('content-item');
          for (let i = 0; i < contentList.length; i++) {
            const item = contentList[i];
            height += item.clientHeight;
            this.listHeight.push(height);
          }
          this.initScroll();
        }
      },
      mounted() {
        this.$nextTick(function() {
          // 由于图片太大，加载比较慢，造成还没有完全加载完就初始化了，导致滚动不了，所以这里加个定时器延迟下
          setTimeout(() => {
            this.getHeightList();
          }, 400);
        });
      },
    });
  </script>
</body>
</html>